Ogurkowski



Feb. 7, 1956 G. oGURKowsKl 2,734,173

FILTER CIRCUIT FOR REMOTE CONTROL INSTALLATION Filed Nov. 19, 1952 United States Patent FILTER CIRCUIT FOR REMOTE CONTROL INSTALLATION Georges Ogurkowski, Zug,-Switzerland, assignor to Landis & Gyr, A. G., a body corporate of Switzerland Application November 19, 1952, Serial No. 321,367 Claims priority, application Switzerland June 23, 1945 1 Claim. (Cl. S33- 70) The present invention relates to a circuit arrangement for the audio-.frequency coupling of two heavy current power circuits, which are normally incapable of being coupled.

Coupling filters are already known, which have a compensating member for the audio-frequency coupling of audio-frequency generators with a power circuit. The combination of two four-terminal networks there employed has the special property that, for the passage of the audio-frequency currents, the input resistance of the lter is equal to the output resistance on the network side. By such an arrangement, with any desired power circuit resistance, no additional inductive and capacitive loads occur, which would involve drawing additional energy from the audiofrequency generator. This condition however only applies in one direction of the energy ow, viz. only from the audio-frequency side towards the mains circuit side, and moreover, only for one narrow band of frequencies.

If now it be desired to couple two power circuits which have diierent frequencies, i. e. are not synchronous or if synchronous have voltage vectors with a constant difference of phase, or because of too great a difference of voltage at any definite place are incapable of being connected and yet are capable of being connected in respect of audio-frequency currents, it is not advantageous to.

connect two coupling filters of the known kind in series and to connect the two remaining output ends with the two mains circuit. Such a solution would be extremely expensive, and take up a great amount of space. Moreover, the audio-frequency current would ow in the reverse direction in one filter, with resultant loss of power.

According to the invention, and in accordance with its object, these diiiculties are overcome and an intermediate coupling filter is provided for the audio-frequency coupling of two heavy current networks normally incapable of being coupled. The invention further permits the audio-frequency current to be transmitted in both directions, and consists of two four-terminal networks which do not allow the power frequency currents to pass and which have connected between them in series a compensating four terminal network in such a manner that, yin either direction of energy ow, the input resistance ofthe whole four-terminal network combination is equal Ito the output resistance thereof.

It will be understood that the foregoing general description and the following detailed description as well are exemplary and explanatory of the invention but are not restrictive thereof.

In the attached drawing an example of embodiment of such a four pole combination is shown. I

Fig. 1 is a diagrammatic representationof a four-pole,

Fig. 2 is a form of embodiment of a four-pole,

Fig. 3 is a four-pole combination and Fig. 4 is a form of embodiment of a four-pole combination according to Fig. 3.

Referring to Fig. 1, let V be any passive four terminal network with sinusoidal voltages applied across the ter- 2,734,173 Patented Feb. 7, 1956 quencies) These quantities will now be evaluated in terms of the. components of the network according to standard methods of network analysis.

Assume V has X branches and N nodes. Then, according to a well known theorem there are X -N +l=n independent meshes (loops) in V, and a complete description of the current flow can be obtained from a consideration of any n independent meshes.

Choose in V any n independent meshes such that mesh l contains E1, mesh n contains En, and the remaining meshes are entirely passive. Equating the voltage drops to the applied voltages this gives a set of n equations.

such that:

where i; is the current in the Ajth loop and the subscript ii referring to the sum of all such elements in the ith mesh and the subscript ij (iej) referring to the sum of all such elements common to the ith and jth mesh. R, L, C, and p have their usual meanings of resistance, inductance, capacitance, and diierentiation with respect to time.

Solution of Equations l gives:

(2) l1=11E11a11tEn In=a1nE1a1mEn where an, am, ann are simple rational functions of the Z13 (2a) given in terms of determinants by:

Mn being the 'minor yof the Ielement Zu'in D. This solution is obtained by a direct application of Cramers rule to (1).

Solving (2) for I1 and E1 in terms of In and En gives:

(3) E1=AEn+BI1r where A, B, C, and D are by denition the elements of the matrix of the network V, and can be computed from (2) by simple algebra to be:

Now the invention itself will be disclosed. Figure 3 is a schematic circuit diagram showing one embodiment of the present invention.

In this drawing, A and B denote two heavy current power circuits normally incapable of being coupled, and for the sake of simplicity only single phase mains are shown. In the circuit A there is included an audiofrequency current generator G1 which operates through a coupling lter KF1 and an isolating switch T1, while in the circuit B another audiofrequency current generator Gz operates through a coupling lter KFz, and an isolating switch T2. The two circuits A and B are each connected to four-terminal networks VP and the latter networks are connected in series with one another through a compensating four terminal network KVP. In this arrangement, the two four-terminal networks VP serve for holding back the power circuit frequency currents from the compensating four-terminal network KVP, and the latter has such properties that the whole four-terminal network combination is adapted to transmit the audiofrequency currents without loss. By means of this arrangement, it is possible to transmit the control currents required from the generator G1 to the circuit B, whilst conversely the control currents from the generator G2 can also be transmitted to the circuit A. Obviously, only one of the two generators is normally in operation, while the other is isolated from its power circuit.

In the embodiment, the terminal resistance Z1 of the four-terminal network combination is formed by the power circuit A, the terminal resistance Z2 is formed by the circuit B; Zei denotes the input resistance towards the circuit A and Zeg denotes the input resistance towards the circuit B.

In accordance with the invention, the input resistance Zez should be equal to the terminal resistance Z2 and Zei should be equal to the terminal resistance Z1.

if M be the matrix of the four-terminal network VP, the two matrices should be constructed equal and should operate in the same manner, thus del wherein the determinant of the matrix 1121 a22 expresses a condition for the passivity of the four-terminal network VP, when it is equal to unity, according to a well known theorem. The matrix of the compensating four-terminal network runs as follows:

since in accordance with the primary assumption the compensating four-terminal network should be passive.

It is known that, 1n the series connection of tourterminal networks, the matrices of the four terminal networks must be multiplied together, in which case the resultant matrix forms the matrix of the series connection. Also in this case, the matrices must be multiplied together in corresponding sequence. We assume provisionally that the elements of the matrix Mk are still unknown and make the assumption that there exists a passive fourterminal network which fulfills the condition that, when connected in series, in the middle of two identical assumed four-terminal networks the matrix product gives the unitary matrix, i. e. it must be (evaluated at the bn biz 1 0U audio-frequency) 1121 1122 b21 bz2 1121 1122 o 1 It is now asserted that the elements of the matrix Mk, i. e. the quantities b11, biz, b21, bz2 can be calculated from the elements of the previously given four-terminal network matrix M, i. e. the quantities au, aia, 1121, azz viz. they are determined from the following equations:

The proof is brought about by calculating out the product of the matrices:

an G12 1111 1112 As will be seen from the above, there results as the product of the matrices actually the unitary matrix, i. e. for a single frequency the combined four-terminal network will allow the desired currents to pass without loss.

Taking into consideration that (6) a11a22-a12a21=1 one nds that (8) b11b22-b12b21=l i. e. that the determinant of the compensating four-terminal network so determined is actually unity.

Now follows a proof that the matrix Mk is always realizable (i. e. a circuit which is purely passive can be constructed which has Mk for its matrix), Whenever the network is made up of only condensers and inductances. This proof does not limit the method to these types of networks, but does prove the general validity of the method in this, the most interesting case.

The following proof makes reference to a particular design for the realization of matrices, but this patent is in no Way limited to circuits designed by this method, and, as shall be shown by example, in most applications it will not be necessary to make use of this method.

To effect the proof, rst right and left-multiply the matrix equation (9) by M inverse (M-l). M will always have an inverse since its determinant is not equal to zero. This gives:

Therefore the matrix Ma will be realizable if the matrix M-1 is realizable i. e. if Vois a four-pole having the matrix M'-1 then the system consisting of two networks Vo connected in series will have the matrix (M1)2.

Now solving Equations 4 so as to get the quantities an, ann, at1n expressed in terms of the elements of the matrix of the network, we have:

alu:-

Now if V1 and V2 are two four terminal networks such that the matrix of V2 is the inverse of' the matrix of V1 and if the matrix of V1 is and hence substitution of the appropriate elements in Equations 13 gives: i

tao'vi--ib-taov. ca

Now if the circuit V is made up` purely of inductances and capacitances, then each term-Zwin Equation-- 1i will be pure imaginary for simple sinusoidal frequencies and hence D and M11 in Equation 2a will be equal to (Dn/c and (Dn-Utl where KandsKlare real quantities. Reference to Equation 2a then shows that an are all pure imaginary numbers. l v

As pointed out in United States Patents 2,067,443 and 2,067,444 to Gewertz the following conditions are bothnecessary and sucient on the quantities an, am, am in order to have a circuit with these as be realizable. We are regarding the as as functions ofthe variable k where Ary-Hw and w=21rf (f is theu frequency) where Re stands for the realpart of.

Now if anUm), anno), 11100) where Ao is the audiofrequency are pure imaginary quantities and satisfy conditions 1, 2, and 3 (since theseare necessary conditions) then -a1I( \o), -ann()\o), -a1n(}\o) also satisfy these conditions and it is obvious there is an infinity of ways in which three functions fnOt), fnn(k)',';f1n(}\) can be constructed such that they satisfy these conditions,T and, take on, respectively, the values. 011100, -ann( \o), 051100) for )\=)\o. Therefore by the sutliciency of these conditions a circuit can be constructed having the desired values to make its matrix the inverse of the matrix M of VP (at \o) whenever VP consists only of capacitances and inductances and therefore Mz=(M-*1)2 is also realizable. l K

In order to further clarify the idea of the invention consider the fourpo1eshown;in-Fig.` 2. Let its matrix bev The elements of the matrix may be evaluated as follows:

For no load we obtain from Equations 3` Now from (15 6 and represents the voltage, transformation ratio. in the case of no load. This ratio can be read: at onceT from Fig.-2. Wehave (16b) shows that ezz is equal tothe current transformation ratio in short circuit; This ratio, also, can be read at once from Fig. 2. The following holds good:

Fig. 4 shows a form of embodiment of a four-pole*-v combination VP-KVP-VP according to Fig. 3 in which the values of the connecting members of the compensationfour-pole KVP were determined` according to the above conditions. This proves at the same time that such a compensation four-pole can be readily. reduced to4 practice.

Let the two four-poles VP bev identical and the connecting members that are provided show the values entered in Fig. 4'. Therefore:

For the matrix elements the following values are found according to the statements made:

tion four-pole KVP:

|Mk|= .2721- (j364) +j2.56510?) .0739 -l-.975s z 1 and from this the determinantal equationsfor the elements of the combination four-poles:

For the control one calculates:

2Z1Z2+Z=2( -i-j284) (-j390) (-72843) 141,000

141,000 9x2- jBgo--l-,7362 The calculated values for Z1 and Z2 for the compensation four-pole KVP are entered in Fig. 4.

(+1472) (-17758) 7 758+ 1.286 =j175s+j 1250 In order to investigate the behavior at the mains frequency of 50 cycles, where at the terminal resistance Z2 the phase voltage of the mains frequency is, say, 28.8 kv., we consider only the right half of the arrangement.

, V:s n

The impedance between the connecting points m, n then amounts to: f

i.k e. the four-pole sought is again passive.

For the determination of the elements we obtain in this Z1= 1.272) -l-j390)= -j496l Fox` the purpose of control we determine The two equal high-pass filters VP may thus be compensated for by one high-pass lter. This is important because it does not cause any change in the frequency characteristics.

By means of the above described lter, the audio- 75 frequency coupling of two asynchronous networks can ma J The above described filter consists solely of inductances, f

capacitors, mutual inductances and resistances, i. e. without any external sources of energy. It is also assumed that the inductances and capacitors employed are free from loss and are linear, i. e. none have a characteristic dependent on the value of the current or of the voltage. Through the said filter arrangement, the control energy can be transmitted without loss, i. e. without additional capacitive or inductive load. This property is especially advantageous when the audiofrequency energy has to be taken over long overhead lines to the intermediate coupling filter. Since the overhead lines have considerable inductive series reactances, a very large inductive load passed through any other intermediate coupling filter would produce such a high voltage drop that the operation of receivers in the coupled network would be rendered impossible by this intermediate coupling.

The invention in its broader aspects is not limited to the specific mechanisms shown and described but departures may be made therefrom within the scope of the accompanying claims without sacrificing its chief advantages.

This application is a continuation in part of my prior application Serial No. 673,503, filed May 31, 1946.

What is claimed is:

In combination, two alternating current power circuits which must be maintained separate for reasons of fre- -quency or phase difference or differences of potential but lwhich must be coupled together for an audio-frequency in connection with control or communication systems,

each power circuit constituting an audio-frequency chari nel, three four-pole passive filter sections connected in series between said power circuits to form an audio-frequency cross-channel between said power circuit channels, said end filter sections having the same matrices, said end filter sections suppressing substantially completely the power frequencies of the power circuits to which they are respectively connected, said intermediate filter section between the end filter sections being a compensating section and having matrix elements of which bu, biz, b21 and bz2 are determined from au, :112, azi and azz of the end filter sections by the relations References Cited in the file of this patent UNITED STATES PATENTS Affel July l, 1924 OTHER REFERENCES Terman: Radio Engineers Handbook, published by McGraw-Hill Book Co., Inc., New York and London, in 1943, pp. 227 and 232. (Copy in Scientific Library.) 

